It is a common requirement in several industries to transport very long and heavy structures across the federal and state highways. As a particular example of such requirement, in the exploration of oil, gas and geothermal energy, drilling operations are used to create boreholes, or wells, in the earth. Drilling rigs used in subterranean exploration must be transported to the locations where drilling activity is to be commenced. These locations are often remotely located and in rough terrain. The transportation of such rigs on state highways requires compliance with highway safety laws and clearance underneath bridges or inside tunnels. Once transported to the desired location, large rig components must each be moved from a transport trailer into engagement with the other components located on the drilling pad.
Moving a full-size rig requires disassembly of the mast into two or three sections which must then be transported. The mast sections are then loaded between a tractor trailer and a dolly system designed to follow the tractor trailer. The dolly systems must follow the tractor in a precise manner or the load will become unstable and dangerous. Safety is a paramount issue. Consistent with the safety issue and the high cost of downtime during transportation is reliability of the system. Breakdowns can be both dangerous and costly if the drilling rig is unavailable. It is also critical to transport the mast sections (or other structural loads) without imparting undue stress on their structures such that the structural strength of the mast is not compromised.
It is also necessary that the transport be simple, have a relatively small turning radius and not require significant programming or balancing of the loads prior to transport. It is also necessary that the system accurately steer the load, such that undesirable wear on the dolly tires and fuel inefficiency can be avoided. It is also desirable that the system requires minimum maintenance and relies on a minimum of hydraulic and electronic functionality.
For example, U.S. Pat. No. 2,167,943 to Fox discloses steering mechanisms for vehicles and more particularly to steering mechanisms between towing and towed vehicles, by which the wheels of the towed vehicle are caused to “track” or follow the paths of the wheels of the towing vehicle in making turns. Fox, however, uses hydraulic components, rather than a simple to implement mechanical linkage steering system, and does not provide for direct control of the dolly with redundant links. As a result, the apparatus of Fox requires more components at the cost of increased weight and complexity. Due to the inclusion of hydraulic assemblies, the apparatus of Fox is less reliable and would require additional maintenance to operate, driving up overall costs for the device.
U.S. Pat. No. 3,403,925 to Sauer discloses a self-centering axle for a vehicle with at least one fixed single or multiple axle, and an oscillatable mobile assembly which includes a wheeled axle for supporting the same and is adapted for attachment to highway-drawn load-carrying vehicles including a chassis adapted to support the load. The apparatus of Sauer does not use simple to implement mechanical steering linkages, but instead relies upon a complex assembly of raceways, clips, arms, and shafts to facilitate steering of the axles. As a result, the apparatus of Sauer may be less reliable and more prone to breakdown as opposed to a simple mechanical linkage steering system. Thus, the apparatus of Sauer suffers from increased costs and reliability issues over a mechanical steering system.
U.S. Pat. No. 3,542,390 to Fikse discloses a tractor and trailer combination, and more particularly to a trailer including a forward and a rear set of opposed lateral support wheels which swivel to facilitate the trailer making a turn with the rear wheels following the arc of the turn. Fikse further discloses a trailer construction with a steerable forward set and a steerable rear set of opposed lateral support wheels or dollies supported upon swivel means. However, the apparatus of Fikse does not provide controllable steering; rather, it relies on interconnected swivels on the rear dollies to facilitate steering of the trailer. The swivel steering system of Fiske provides a less accurate and less stable method for steering as opposed to a mechanical linkage steering system.
U.S. Pat. No. 4,117,905 to Mustered discloses a hydraulic articulated steering system with an equivalent total hydraulic steering system for back-up, emergencies, and for supplementary additional steering power, and without dependence upon additional mechanical linkages. Specifically, Mustered discloses a steering system comprised of steering actuation means and two or more hydraulic telescoping steering means, each of which is positioned proximate to the pivot attachment point of the articulated vehicle with at least one of the two or more hydraulic steering means positioned on a first side of this pivot attachment point and another of the hydraulic telescoping steering means positioned on the first or second side of the pivot attachment. The dual metering control means of Mustered is more complex than a simple mechanical steering linkage, and as a result may provide less reliable steering operation over time. Because Mustered relies upon a hydraulic steering system, it does not provide for direct control of the dolly with redundant mechanical links. Thus, the apparatus of Mustered provides less accurate steering as well as increased weight and complexity over a mechanical linkage steering system. Furthermore, cost and reliability of the steering device is adversely affected.
U.S. Pat. No. 4,441,730 to Damm discloses a steering device for a multi-axled goose-neck trailer coupled with a vehicle in front of the trailer, the steering device comprising wheels pivotable about a main axle and connected to stay rods for forcibly steering the rear wheel set through hydraulics in a direction opposite to the steering wheels of the tracking vehicle, so that the trailer more closely follows the track of the tracking vehicle. The apparatus disclosed in Damm would thus put substantial strain and wear on the rear wheels. Further, the use of hydraulic cylinders in Damm for forcibly steering of the rear wheels may lead to faster deterioration of the steering assembly and hydraulics in addition to the increased wear on the wheels. The use of hydraulics further increases the overall weight and costs of the steering system, and also adversely affects reliability of the system.
U.S. Pat. No. 5,035,439 to Petrillo discloses a tractor trailer or other vehicle that is equipped with an auxiliary rear steering arrangement which is steered via pneumatic-type suspensions and hydraulic cylinders as well as adjusting the weight of the trailer and load to facilitate steering. The apparatus of Petrillo requires an operator, and is generally directed more towards a more efficient method of weight distribution for the load. In this regard, the apparatus taught by Petrillo provides for a less accurate steering system as opposed to a direct mechanical linkage steering system, and has added drawbacks of increased weight and potential reliability problems due to the use of hydraulics and pneumatics.
U.S. Pat. No. 5,234,069 to Krone et al. discloses a steering control system in which one pair of wheels of an articulated steering vehicle are steered in synchronization with the articulation steering and controlled via a pump and valve means for directing fluid to hydraulic cylinders, which are locked in place. The hydraulic steering system of Krone is therefore more complex and prone to failure than a simple mechanical linkage steering system. The hydraulic steering system of Krone further suffers from added weight of the hydraulic assemblies and increased costs as a result.
U.S. Pat. No. 5,479,999 to Proia discloses an automatic powered, self-tracking system with powered controls for the rear axles of large vehicles, along with the use of motion detectors to sense the direction and degree of vehicle turning, and are connected to a plurality of either hydraulic or pneumatic axle-pivoting mechanisms which exert a force on preselected components of a vehicle's suspension system. As a result, the steering apparatus taught in Proia is highly dependent upon use of motion detectors, and the failure of any one of the motion sensors would have a substantially adverse impact on the accuracy of the system. In addition, the use of hydraulics and pneumatics on the apparatus of Proia induces increased weight and costs on the system, drawbacks that are not present in a simple mechanical linkage steering system.
U.S. Pat. No. 5,700,023 to Picard discloses an articulated vehicle composed of a series of modules interconnected by a composite articulated connection comprising at least one elastic articulation with controlled movement. Picard further discloses a vehicle articulated in a simple mechanical fashion, making it possible to ensure better relative maintenance in position of the modules of which it is composed near-perfect following of the curves and irregularities in the roadway, and a substantial limitation of extraneous movements of the modules relative to each other, even for road trains composed of two or more modules. While Picard discloses a method of mechanical self-tracking, its steering system is unable to achieve precise articulation for precise steering and navigation of the dolly.
U.S. Pat. No. 6,152,475 to Poole discloses a converter dolly that replaces the rear wheels of a truck trailer to provide the trailer with a steering ability about its rear wheels, and is controlled by the driver of the tractor through a control system mounted in the tractor cab. The converter dolly is modified to include a hydraulic actuating system, including a piston, cylinder, and pump assembly, which act upon the tongue of the converter dolly to pivot the converter dolly about a king pin. Thus, Poole suffers several deficiencies from the use of hydraulics, such as increased costs associated with the hydraulics as well as increased weight of the hydraulic assemblies. Additionally, the increased complexity of the steering system disclosed in Poole renders it more prone to reliability issues and failures and further requires that the driver of the tractor manually operate the dolly steering system.
U.S. Pat. No. 7,412,315 to Wildey et al. discloses a steering system for an articulated vehicle that has a microprocessor connected to a proportional solenoid valve which controls the direction, amount and rate of flow of hydraulic fluid to and from hydraulic articulation cylinders, which provide articulation between the frames of the articulated vehicle. Wildey also features a positional feedback sensor to measure the angle of articulation between the frames and communicates the angle of articulation to the processor. In Wildey, the use of solenoids in combination with hydraulics for control and articulation of the steering assembly leaves it more prone to failure over more reliable mechanical linkage steering systems and does not allow for direct control of the dolly. Thus, the steering system of Wildey provides less accurate steering as well as increased weight and complexity over a mechanical linkage steering system.
U.S. Pat. No. 7,637,512 to McGhie et al. discloses a boom support vehicle which reduces tire scuffing, reduces structural size, and provides improved turning characteristics. McGhie includes a self-steering castor axle as the front axle of the boom support vehicle front dolly, similar to the castor axle of some three axle semi-trailers, a two member articulated boom support vehicle design which has an articulation point (steering pivot) near the rear of the vehicle. While the dolly steering system disclosed in McGhie is separate from the tractor, it fails to disclose an automatic steering system, but rather relies upon the turning forces on the front axles to facilitate the steering and characteristics upon the back axles. Further, the apparatus of McGhie contains conventional rear axles which are not steerable and merely follow the tracking provided by the front axles.
Thus, there remains a need for improvements for the creation of a safe and reliable dolly system for transporting large structural loads on the federal and state highway systems. In particular, it is desirable to transport large loads on a mechanically steered articulating dolly system having a relatively small turning radius.
It is further desirable to have a dolly device that is relatively inexpensive to produce and implement, as well as inexpensive to maintain with a high degree of reliability. It is also desirable that such a dolly device would also be relatively lightweight in order to reduce consumption of fuel during transport of the dolly and payload.
In summary, the preferred embodiments of the present invention provide a unique solution to the engineering constraints and environmental challenges of providing a durable mechanically actuated steering system.